The invention relates to a gear shifting drum for a gear shifting device of variable-speed gearboxes for motor vehicles, with an outer surface area of the cylindrical gear shifting drum having at least one curved path for form-fitting guidance of an engagement member of a gearshift fork, wherein the gearshift fork is connected to a gearshift sleeve of a synchronization device which is arranged for axial displacement between two gears on a gearbox shaft disposed in parallel relation to the gear shifting drum.
A gear shifting device including a gear shifting drum of the above-stated type is described in the magazine xe2x80x9cauto motor sportxe2x80x9d, edition 7/1995, pages 98 to 100. The gear shifting drum replaces a commonly used H gearshift, whereby unlike the conventional gearshift, the single shift stages, i.e. the gears, are shifted sequentially in a row or plane. The gear control lever returns to its initial position after engaging a gear so as to be available for shift to a next gear. In this manner, it is possible to use a reverse motion of the gear control lever for a upshift and a forward movement from the initial position for a downshift. The gear shift mechanism provided with a gear shifting drum prevents a bypassing of gears because a shift from an engaged gear can only be carried out to the neighboring gear, i.e. the next higher or next lower gear. Translation of the motion as triggered by the gear control lever to a rotary motion of the gear shifting drum for realizing a gear change is effected by an electric control motor by which the shift impulses, triggered by the gear control lever, are translated in a defined rotary motion of the gear shifting drum. As a consequence of the positive fit of the gearshift fork in the curved path of the gear shifting drum, a turn of the gear shifting drum results in an axial displacement of the gearshift fork which is connected with a gearshift sleeve of the synchronization device. The conventional gear shifting drum includes a cylindrical base body having an outer surface area formed with a curved path. The gear shifting drum known from the prior art is made from solid material through a material-removing process, in particular through a profile milling machine. Such a gear shifting drum is complicated to manufacture, incurs high manufacturing costs and has a relatively high weight which runs counter to the demand for lightweight construction.
It is an object of the invention to provide a gear shifting drum which, compared to the state of art, has a curved path made in a cost-efficient manner and is advantageous with respect to weight concerns.
This object is attained in accordance with the invention by the subject matter of claims 1 and 2.
The invention according to claim 1 provides for a gear shifting drum which has at least one wall on its outer surface area for formation of a curved path, with the wall extending radially outwards from the outer surface area. Such a gear shifting drum may be formed, for example, by a hollow cylindrical sheet metal body whereby a sheet metal strip circumscribes the cylindrical body and is permanently attached to the outer surface area, for example by welding or soldering, for formation of the wall. The wall has a circumferential area which is profiled in accordance with the configuration of the curved path.
According to the invention set forth in claim 2, the gear shifting drum includes a hollow cylindrical base body which is surrounded in concentric relation by a cylindrical sleeve formed with the curved paths. This measure permits the continuous use of same base bodies which can be combined with sleeves having differently configured curved paths. Thus, this invention offers, for example, to the gearbox manufacturer, for purposes of cost reduction, the option to increase the stock of same components. A positionally fixed arrangement on the base body can be realized when securing the sleeve, for example by welding, soldering or gluing.
Common to both inventions is a concept of the gear shifting drum to significantly reduce the complexity of manufacture. The invention set forth in claim 1 eliminates any material-removing process for providing the curved paths. The further invention set forth in claim 2 relates to a gear shifting drum which is so designed that the required material-removing process to form the curved path can be significantly reduced compared to the known prior art.
Further features of the invention are subject matter of the dependent claims 3 to 14.
According to an aspect of the invention set forth in claim 1, the gear shifting drum includes for formation of a curved path two walls in spaced-apart relation for guiding the engagement member of the gearshift fork. As an alternative, which optimizes the structural design, the invention includes also a curved path which is made from one wall on which the engagement member of the gearshift fork is guided by means of a forked projection.
In accordance with the invention, a cylindrical base body is provided as gear shifting drum and has an outer surface area for permanent attachment of pairs of perforated spaced-apart disks of undulating profile, whereby these disks, which form a curved path, are permanently secured to the circumference of the base body. As an alternative to the perforated disks, the curved paths of a gear shifting drum can be provided by means of a square or rectangular profiled strand or round profile, whereby respectively two paired profiles are arranged on the circumference of the outer surface area of the base body.
Preferably, the curved path of the gear shifting drum can be further constituted by a single-piece U-shaped profile which corresponds to the configuration of the curved path and is secured to the circumference of the base body. The spacing between both legs of the U rail is thereby suited to the required width dimension of the engagement member of the gearshift fork. This U rail reduces the required manufacturing costs and, moreover, contributes to a reinforcement of the gear shifting drum which thus can be optimized with respect to weight by reducing the wall strength.
A defined length of the curved path can be realized by so designing the walls of the gear shifting drum that their end zones are closed, i.e. turned inwardly with respect to one another to thereby form a stop for the engagement member of the gearshift fork.
Suitable for the manufacture of the base body for the gear shifting drum is, preferably, a tubular body of sheet steel having end faces closed by lids of sheet steel. The inherent stiffness of the gear shifting drum, of the positional securement, as well as the attachment to the base body can be enhanced by designing the lids of preferable pot-shaped configuration.
According to a further feature of the invention, the lids are each provided with an axially projecting central pin to permit a rotating arrangement of the gear shifting drum in the gearbox housing. The pin may be formed in one piece with the lid or may constitute a separate component which is permanently secured to the lid.
Rotation of the gear shifting drum in dependence on the movement of the gear control lever is realized, preferably, by a control motor which executes a defined and precise turning of the gear shifting drum by means of a geared connection. The gear shifting drum includes thereby outer teeth for direct engagement of a gear of the control motor. As an alternative, the translation of a rotary motion between the control motor and the gear shifting drum can also be realized by a gear rack. The outer teeth of the gear shifting drum may be implemented by, for example, correspondingly designing one of the end lids at the end face. Also suitable is a separate ring provided with outer teeth and circumscribing the gear shifting drum.
An improved shifting accuracy of the gear shifting drum can be accomplished by connecting the gear shifting drum with a locking device which ensures an exact rotational locking of the gear shifting drum in dependence to the gear being engaged. The locking device may be formed, for example, by providing a lid with dome-shaped recesses or impressions for interaction with a spring-loaded spherical locking member which is positioned in the gearbox housing. The locking device may further be provided with a switch for optical display of the actually engaged whereby an interaction is provided between a particularly designed, especially recessed impression which is assigned to the reverse gear position and a spherical locking member of the locking device with the spherical locking member applying of an increased stroke. This particular locked position, which is assigned to the reverse gear, can be used in conjunction with a switch for actuation of a motor vehicle switch for a tail light.
A weight reduction can be realized in accordance with the invention by making the base body of the gear shifting drum from plastic material or light metal, and by securing the walls through gluing or another permanent attachment procedure, to the base body for making the curved paths.
According to an aspect of the invention, set forth in claim 2, the base body and the coaxial sleeve of the gear shifting drum are made from different materials. Optimization of weight can be realized by making the base body from plastic material and the complementary sleeve from steel for strength reasons and for improving the wear resistance.